Protecting groups alcohol protection

Protection of hydroxyl groups. Alcohols are converted into SEM ethers in high yield on reaction with 1 and diisopropylethylamine. Deprotection is effected by treatment with h-Bu4NF in THF or HMPT at 45°. 

Protection of hydroxyl groups. Alcohols and phenols react with 1 and tri-ethylamine to form tetrahydro-2-furanyl (THF) ethers (85-98% yield). The reaction of acids with 1 results in THF esters. These derivatives are stable to base and nucleophilic reagents they are readily removed by acid-catalyzed hydrolysis or methanolysis. One synthetic application is conversion of the ethers into alkyl bromides by reaction with triphenyphosphine dibromide (1,1247-1248), a reaction that is faster than that with the free alcohols. 

Protection and deprotection of functional groups. Alcohols and their tetrahydro-pyranyl ethers are interconverted with iodine as catalyst. Etherfication is done in a nonhydroxylic solvent, whereas the ether cleavage is achieved in MeOH. 

Protection of hydroxy groups. Alcohols (primary, secondary, tertiary) can be protected as j3-methoxyethoxymethyl (MEM) ethers. These ethers can be prepared by reaction of (1), slight excess, with either the sodio or lithio derivative of the alcohol in THF or DME at 0° (argon). Alternatively, the ethers can be prepared by the reaction of (1) with alcohols in the presence of ethyldiisopro-pylamine. A third method for etherification is reaction of alcohols with the triethylammonium salt of (1), CH30CH2CH20CH2N (C2H5)3C1, in CH3CN at reflux. Yields by the three methods are >90%. 

Silyl ethers have an important role as hydroxyl-protecting groups/ Alcohols can be easily converted to trimethylsilyl ethers by reaction with trimethylsilyl chloride in the presence of an amine or by heating with hexamethyldisilazane. Although these are useful compounds when the objective is preparation of a less polar derivative of... 

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